The present invention relates to semiconductor devices of multiple-chip configuration having capacitive insulation means for electrical separation and isolation between primary side circuitry and secondary side circuitry while permitting signal transmission therebetween and also relates to integrated circuits employing the devices and, in more particular, to communication terminal apparatus including an analog front end (AFE) and/or a modulator/demodulator, called “modem.”
Traditionally, individual or “discrete” electronics components such as transformers or photo-couplers, also known as insulating couplers or isolators among those skilled in the art, are typically employed in cases where electrical insulation/isolation is to be established between a plurality of circuits while permitting signal transmission between them. For instance, in the field of communications technologies, higher dielectricity has been strictly required at boundaries between networks and terminals in order to provide enhanced protection for network facility with high publicities and also for terminal devices operatively associated therewith. To this end, isolators such as small-size communication-use transformers have been used. Alternatively in the fields of measurement technologies and medical industries, isolators have been used as means for providing electrical insulation and isolation between a signal detection unit and a signal processing unit, such as between a sensor module and its associative signal waveform processor circuitry, in a viewpoint of the safety for human bodies and measurement equipment with enhanced anti-noise performances.
In the case of using transformers to provide electrical insulation required, the quest for reduction in size and in weight is limited due to the presence of restrictions against materials and structures used, while accompanying a penalty as to unwanted cost/price increases. Isolators using a photo-coupler with a combination of light-emitting element and photosensitive element for detection of light received are generally small in size and less in weight and also low in price. Unfortunately such photocoupler can readily vary in electrical characteristics thereof with a change in temperature or other parameters. Compensating for such characteristic deviation does require the use of a correction circuit, which in turn requires highly accurate control techniques. Another problem faced with the photocoupler-based isolators is that extra fabrication processes for manufacturing the light emitting and receiving elements should be required in addition to standard or ordinary fabrication processes in the manufacture of a semiconductor device.
Discrete components for constitution of insulation barriers include a ceramic capacitor for electric power supply or for serge protection. A signal transmission circuit using capacitors of this type is called the capacitive insulation amplifier or, alternatively, capacitive insulation coupler among those skilled in the art to which the invention pertains. Known methodology for signal transmission via such capacitive insulation barriers includes pulse width modulation (PWM) schemes. One typical signal transfer technique using three separate capacitive insulation barriers has been disclosed in Published Japanese Patent Application No. 7-307708 (corresponding to U.S. Pat. No. 5,654,984), along with a model application circuit using the barriers.